Rapid thermal processing (RTP) is rapidly becoming the technology of choice for oxidation and annealing steps in advanced ultra-large scale integration (ULSI) fabrication. The ability to subject the wafer to short (typically less than 60 sec.), high temperature (500-1200.degree. C.) heat treatments leads to significant device performance improvement over an equivalent process performed in a high temperature furnace. Ramp rates for most RTP systems range from 20-100.degree. C./s compared to 5-10.degree. C./min for a conventional furnace. The high ramp rate capability of the RTP system provides a significant advantage over a furnace. For example, a RTP process for source/drain annealing which is typically performed at 950-1050.degree. C. for 30 s provides much higher dopant activation, lower residual damage and shallower junctions compared to an 850.degree. C., 30 min. anneal in a furnace. Similarly, thin thermal oxides grown by RTP at 1000-1050.degree. C. are more reliable than those grown at 850-900.degree. C. in a furnace. The short thermal cycle of RTP makes it possible to grow oxides or anneal implants without significant redistribution of dopants. Another advantage of RTP over a conventional furnace is better ambient control (i.e. lower contamination) and reduced processing pressures. Thus, nitrided oxides which are obtained by growing oxides in a NO/O.sub.2 or a N.sub.2 O/O.sub.2 ambient can easily be grown by RTP. RTP also provides a significant advantage for titanium silicide formation and anneal. Increasing formation temperature, while reducing the formation time, increases the ratio of silicide to TiN that is formed, while also reducing undesirable lateral overgrowth. A 650-700.degree. C., 30-60 s RTP silicide formation provides a thicker silicide than a 550-600.degree. C. 30-60 min. furnace process. RTP also plays an important role in silicide annealing. During silicide formation, the high resistivity C49 phase is created and must be transformed to the lower resistivity C54 phase by annealing. Since the activation energy for this transformation is fairly high, and increases with decreasing feature size, a high temperature anneal at 800-850.degree. C. is necessary to accomplish the transformation. However, a short (15-30 s) process time must be used to prevent uptake of dopant from the underlying material into the undoped silicide. RTP is also suitable for CVD processes, since higher temperatures can be used to enhance the deposition rates and hence throughput. RTP also enables the use of single wafer processing and associated single wafer process control. Single wafer processing is clearly gaining ground as the need to cluster processes and increase wafer size grows.
Despite the process advantages, RTP systems are plagued primarily by equipment limitations. The biggest bane is temperature control and uniformity. The slow ramp rates of a furnace ensure that all elements are in thermal equilibrium which results in a uniform temperature distribution. In an RTP system, only the wafer is directly heated, while the reactor chamber and the ambient remain cool. High temperature ramp rates can be achieved because of direct wafer heating, but this also results in large temperature gradients in the RTP system. Typically, elaborate multi-zone lamps arranged in a linear or circular array are used to radiantly heat the wafer. The multi-zone lamps are typically located directly above or below the wafer. Multi-point pyrometry is necessary to measure wafer temperature distribution across the wafer and to control the power to each of the lamp zones, so that uniform wafer temperature distribution is obtained. Non-uniform wafer emissivity, wafer to wafer variation in emissivity, and variation of wafer emissivity with temperature further complicate uniform wafer heating and pyrometric temperature measurement. Although engineering solutions have been developed for many of these problems, they generally increase system cost and complexity.